Inner districts of large cities normally have very narrow streets and, therefore, there is little or no possibility of vehicles, particularly large vehicles maneuvering in those small areas. Thus, the maneuverability of utility vehicles, particularly ones of large loading capacity and dimensions is of increasingly great importance, especially particularly in inner districts of cities.
The reasons for this are that (a) for historical reasons, the inner districts are generally densely built, with narrow, winding streets and sharp-angled turns; (b) due to the increasing traffic density and parked vehicles traffic frequently ties up intersections; and (c) the slowing down of traffic such as by traffic islands, speed bumps, and narrowed roadways to limit the speed of vehicles, all greatly limit traffic movement, in view of the increasing extent of landscaping of traffic-free areas, less and less space remains available for vehicular traffic.
Since the inner regions of larger cities represent a concentration of industrial and business, as well as residential districts, considerable disadvantages for deliveries service and garbage removal services are burdens on such city districts due to their restricted traffic conditions. This can have a disadvantageous effect on the economic structure of such city districts. Since the handling of the deliveries and of garbage removal requirements of business and residential districts calls for an increasingly greater transportation capacity, larger transport vehicles are required for these activities. These larger vehicles have particularly larger problems in navigating within the decreasing space, because due to their large dimensions, vehicles are less maneuverable and require more room for maneuvering.
A number of vehicle manufacturers, particularly of utility vehicles used in the municipal field such as garbage trucks and street sweepers, have attempted to meet the requirements for the elimination of these problems. Thus various means are employed from a reduction in the loading capacity of the vehicles, all the way to technical improvements in maneuverability. The reduction in loading capacity, i.e. the reduction in transporting capacity, requires the use of additional vehicles, particularly for municipal use, which must then transfer their load to larger vehicles for further transportation thereof. This results in higher reloading costs, increased cost of personnel, increased interference with traffic in congested central areas to the larger number of vehicles, increased energy consumption, and increased air pollution.
One known improvement in the provision of greater maneuverability of large capacity vehicles, has been by providing a street sweeping machine with an all wheel steering capability. Such a street sweeping machine, is sold by RAMO Kommunal Fahrzeuge GmbH of Germany. It has a small turning radius and can maneuver in small spaces. All wheel steering offers considerable advantages in all driving and maneuvering situations, and enables a faster and more accurate control of the complicated traffic patterns in the inner city, but it has one decisive disadvantage. Due to the narrow parking spaces, vehicles of this kind approach the curbs of the sidewalk laterally. If the driver, with his all wheel steering, now steers strongly to the side away from the curb to move out of a parking space, the steered rear wheel of the all wheel steering hits the curb and rides over it. When the vehicle is heavily loaded it can damage the sidewalk, strike a sign or lamp post with the rear of the vehicle, and even hit pedestrians. It has been suggested to increase the field of view of the driver, but that cannot remedy this problem. The driver is too busy and cannot continuously note whether and when the steering of the rear wheels should be active or be deactivated, especially since in these situations the region to the rear with its moving traffic must also be observed.
It is also known to install means for detecting and optically displaying the steering angle of a steered wheel of a motor vehicle. German published patent application No. 4,035,794 discloses a device for optically displaying the steering angle of a steered wheel and the direction of travel of the vehicle. One disadvantage of this device is that the display does not automatically intervene in the steering or driving process but merely passively informs the driver of the detected steering angle. If the preprogrammed value of the steering angle is exceeded, the driver is advised of this by a sound alarm.
German published patent application No. 4,233,624 discloses a distance warning having an optical sensor system which detects an object or a vehicle that is within a preselected minimum distance, and gives the driver a suitable warning signal when the distance is less than the preprogrammed minimum. This device is also merely a passive parking aid and does not intervene in the steering of the vehicle.
German published patent application No. 3,438,021 discloses a control system for vehicles in which, electronic data processing and control systems are used to control the relationship of the steering angle of a rear wheel to the position of the front wheel, in accordance with the speed of the vehicle. The control system has a detector for forward travel which the steering angle is recorded in accordance with the speed of the vehicle, but this action can take place only if forward travel of the vehicle is maintained for a predetermined period of time. This apparatus, while having advantages of an automatic control device, has the disadvantage that upon the vehicle approaching obstacles, no assistance and adjustment signal is provided to the control mechanisms.
Similar information is provided by German published patent application No. 3,903,834 which is used on a automobile with four-wheel steering, and signals are obtained from various sensors about the steering of the front and rear wheels, and are transmitted to a computer. The computer acts on sensor abnormalities and thereby actuates power steering to improve the side steering of the front wheels and also controls the speed of the vehicle during the steering to achieve an accident free operation.
U.S. Pat. No. 4,955,443 discloses a similar system of computer controlled four wheel steering of motor vehicles.
The devices of the prior art have the feature in common that they do not provide any indication for controlling the steering of the rear wheels of an all wheel steering, and the rear wheels are controlled and moved separately from the front wheels. No prevention is provided against hitting existing obstacles and against driving over them. Such endangering of the surrounding area can result from the fact that upon steering the vehicle in a steady direction, and particularly when going around a curve, the steering of the wheels of the rear axle, actuated by the sensors, responds upon approach to an obstacle and the vehicle is steered out of the continuous direction of movement with the rear of the vehicle swinging out in the direction away from the obstacle and thus exposing other traffic the vehicle and itself to the danger of a collision. Another disadvantage is that, in the case of proportionally adapted steering motion of the two axles of the all wheel steering, upon movement of the front axle out of the continuous direction of movement, such as when steering around a curve from a forward travel of the vehicle, the wheels of the rear axle would follow the steering movement of the front axle. Since this is an interruption of a continuous movement, the wheels of the rear axle would no longer follow the previous direction of travel upon a change in the direction of movement, as a result of the all wheel steering the rear wheels follow the position of the wheels of the front axle, and can collide with an obstacle, such as a street corner curb.
In vehicles with engaged all wheel steering, there are considerable difficulties in getting out of narrow parking places spaces without extensive steering maneuvers. Vehicles without all wheel steering can free themselves more easily from such constricted spaces. There are no devices known which permit adaptation of the steering positions of vehicles with all wheel steering from narrow spaces, which move the rear wheels of the all wheel steering past an obstacle.